memcg: drain obj stock on cpu hotplug teardown

Currently on cpu hotplug teardown, only memcg stock is drained but we
need to drain the obj stock as well otherwise we will miss the stats
accumulated on the target cpu as well as the nr_bytes cached. The stats
include MEMCG_KMEM, NR_SLAB_RECLAIMABLE_B & NR_SLAB_UNRECLAIMABLE_B. In
addition we are leaking reference to struct obj_cgroup object.

Link: https://lkml.kernel.org/r/20250310230934.2913113-1-shakeel.butt@linux.dev
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8f9b35f80e24efeea787e902765900a905d620be..a037ec92881d59c3aca3658fc314d2bac092c694 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1921,9 +1921,18 @@ void drain_all_stock(struct mem_cgroup *root_memcg)
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
        struct memcg_stock_pcp *stock;
+       struct obj_cgroup *old;
+       unsigned long flags;
 
        stock = &per_cpu(memcg_stock, cpu);
+
+       /* drain_obj_stock requires stock_lock */
+       local_lock_irqsave(&memcg_stock.stock_lock, flags);
+       old = drain_obj_stock(stock);
+       local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+
        drain_stock(stock);
+       obj_cgroup_put(old);
 
        return 0;
 }